System and method for chemically cooling an ablation antenna

ABSTRACT

A method of performing an ablation procedure includes the steps of inserting an antenna assembly into tissue and supplying energy thereto for application to tissue. The method also includes the step of causing contact between a first material and at least one other material disposed within the antenna assembly to thermally regulate the antenna assembly. According to another embodiment, an ablation system includes an energy delivery assembly. A first chamber is defined within the energy delivery assembly and is configured to hold a first chemical. Another chamber is defined within the energy delivery assembly and is configured to hold at least one other chemical. The first chamber and the other chamber are configured to selectively and fluidly communicate with each other to cause contact between the first chemical and the at least one other chemical to cause an endothermic reaction and/or an exothermic reaction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 12/787,639, filed on May 26, 2010, the entirecontents of which are incorporated by reference herein.

BACKGROUND

1. Technical Field

The present disclosure relates generally to microwave antennas used intissue ablation procedures. More particularly, the present disclosure isdirected to a microwave antenna having a coolant assembly for chemicallycooling the microwave antenna.

2. Background of Related Art

In the treatment of diseases such as cancer, certain types of cancercells have been found to denature at elevated temperatures which areslightly lower than temperatures normally injurious to healthy cells.These types of treatments, known generally as hyperthermia therapy,typically utilize electromagnetic radiation to heat diseased cells totemperatures above 41° Celsius while maintaining adjacent healthy cellsat lower temperatures where irreversible cell destruction will notoccur. Other procedures utilizing electromagnetic radiation to heattissue also include ablation and coagulation of the tissue. Suchablation procedures, e.g., such as those performed for menorrhagia, aretypically done to ablate and coagulate the targeted tissue to denatureor kill the tissue. Many procedures and types of devices utilizingelectromagnetic radiation therapy are known in the art. Such therapy istypically used in the treatment of tissue and organs such as theprostate, heart, kidney, lung, brain, and liver.

Presently, there are several types of microwave probes in use, e.g.,monopole, dipole, and helical, which may be inserted into a patient forthe treatment of tumors by heating the tissue for a period of timesufficient to cause cell death and necrosis in the tissue region ofinterest. Such microwave probes may be advanced into the patient, e.g.,laparoscopically or percutaneously, and into or adjacent to the tumor tobe treated. The probe is sometimes surrounded by a dielectric sleeve.

However, in transmitting the microwave energy into the tissue, the outersurface of the microwave antenna typically heats up and mayunnecessarily effect healthy tissue immediately adjacent the antennaouter surface. This creates a water or tissue phase transition (steam)that allows the creation of a significant additional heat transfermechanism as the steam escapes from the local/active heating area andre-condenses further from the antenna. The condensation back to waterdeposits significant energy further from the antenna/active treatmentsite. This local tissue desiccation occurs rapidly resulting in anantenna impedance mismatch that both limits power delivery to theantenna and effectively eliminates steam production/phase transition asa heat transfer mechanism for tissue ablation.

To prevent the unintended effects on adjacent tissue, several differentcooling methodologies are conventionally employed. For instance, somemicrowave antennas utilize balloons that are inflatable around selectiveportions of the antenna to cool the surrounding tissue. Thus, thecomplications associated with unintended tissue effects by theapplication of microwave radiation to the region are minimized.Typically, the cooling system and the tissue are maintained in contactto ensure adequate cooling of the tissue.

Other devices attempt to limit the heating of tissue adjacent theantenna by selectively blocking the propagation of the microwave fieldgenerated by the antenna. These cooling systems also protect surroundinghealthy tissues by selectively absorbing microwave radiation andminimizing thermal damage to the tissue by absorbing heat energy.

SUMMARY

According to an embodiment of the present disclosure, a method ofperforming an ablation procedure includes the steps of inserting anantenna assembly into tissue and supplying energy to the antennaassembly for application to tissue. The method also includes the step ofcausing contact between a first material and at least one other materialdisposed within the antenna assembly to thermally regulate the antennaassembly.

According to another embodiment of the present disclosure, a method ofperforming an ablation procedure includes the steps of inserting anantenna assembly into tissue and supplying energy to the antennaassembly for application to tissue. The method also includes the stepsof causing contact between a first chemical held within a first chamberdefined within the antenna assembly and at least one other chemicaldisposed within at least one other chamber defined within the antennaassembly to cause one of an endothermic reaction and an exothermicreaction to thermally regulate the antenna assembly.

According to another embodiment of the present disclosure, an ablationsystem includes an energy delivery assembly configured to deliver energyfrom a power source to tissue. A first chamber is defined within theenergy delivery assembly and is configured to hold a first chemical. Atleast one other chamber is defined within the energy delivery assemblyand is configured to hold at least one other chemical. The first chamberand the at least one other chamber are configured to selectively andfluidly communicate with each other to cause contact between the firstchemical and the at least one other chemical to cause one of anendothermic reaction and an exothermic reaction to thermally regulatethe energy delivery assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic diagram of the microwave ablation system accordingto an embodiment of the present disclosure;

FIG. 2 is a perspective, internal view of a microwave antenna assemblytaken along line X-X according to an embodiment of the presentdisclosure;

FIGS. 3A and 3B are cross-sectional views taken along line X-X of themicrowave antenna assembly of FIG. 1 according to various embodiments ofthe present disclosure;

FIG. 3C is a perspective view of a component detailing operation of themicrowave antenna assembly of either FIGS. 3A and 3B; and

FIG. 4 is a cross-sectional view of a microwave antenna assemblyinserted into tissue according to another embodiment of the presentdisclosure.

DETAILED DESCRIPTION

Embodiments of the presently disclosed apparatus are described in detailbelow with reference to the drawings wherein like reference numeralsidentify similar or identical elements in each of the several views. Inthe discussion that follows, the term “proximal” will refer to theportion of a structure that is closer to a user, while the term “distal”will refer to the portion of the structure that is farther from theuser.

Generally, the present disclosure is directed to a microwave antennaassembly having an energy source or generator adapted to deliver energyto tissue via the antenna assembly. The antenna assembly includes one ormore chambers configured to receive and accommodate suitable chemicals(e.g., fluid, solid, a fluid and solid combination) therein that, uponmutual contact, mixture, dissolving, or reaction with each other, causeeither an endothermic reaction or exothermic reaction depending on thechemicals used. Two or more chemicals are disposed within individualsealed chambers disposed within the antenna assembly. Through use ofvarious methods of the various embodiments of the present disclosure,the chemicals are caused to contact each other at the appropriate time(e.g., during a tissue ablation procedure), thereby causing anendothermic or exothermic reaction, depending on the chemicals used. Forexample, the individual chambers holding the chemicals may be separatedby a breakable membrane. In this scenario, the antenna assembly may besemi-flexible or semi-rigid such that the antenna assembly may be flexedor bent at the appropriate time to cause the membrane to break, therebyallowing the previously separated chemicals to contact each other andcause either an endothermic or exothermic reaction. Additionally oralternatively, the individual sub-chambers holding the chemicals may beseparated by a mechanical interface configured to selectively causecommunication between the sub-chambers through use of an actuationinterface disposed on the antenna assembly.

Embodiments of the present disclosure may also be implemented using amicrowave monopolar antenna or other suitable electrosurgical devicessuch as, for example, radiofrequency monopolar and/or bipolarelectrodes, an ultrasound transducer, laser fiber, a direct current (DC)heating element, or the like, and may be implemented in operablecooperation with any suitable energy source (e.g., radiofrequency,direct current, microwave, laser, ultrasound, etc.).

In the scenario wherein an endothermic reaction results from contactbetween the two or more chemicals, the antenna assembly and/orsurrounding tissue is cooled by the endothermic reaction. In use, whilethe antenna assembly is placed relative to the desired tissue site, theheat generated by the application of microwave energy from the antennaassembly to tissue may be cooled by causing an endothermic reactionwithin the antenna assembly. In the scenario wherein an exothermicreaction results from contact between the two or more chemicals, theantenna assembly and/or surrounding tissue is heated by the exothermicreaction. In use, while the antenna assembly is placed relative to thedesired tissue site, surrounding tissue such as, for example, theinsertion tract resulting from the insertion of the antenna assembly oran introducer into the tissue, may be heated or cauterized to stopbleeding or prevent tumor cells from “seeding” the insertion tract.

FIG. 1 shows a microwave ablation system 10 that includes a microwaveantenna assembly 12 coupled to a microwave generator 14 via a flexiblecoaxial cable 16. The generator 14 is configured to provide microwaveenergy at an operational frequency from about 300 MHz to about 3000 MHz,although other suitable frequencies are also contemplated.

In the illustrated embodiment, the antenna assembly 12 includes aradiating portion 18 connected by feedline 20 (or shaft) to the cable16. More specifically, the antenna assembly 12 is coupled to the cable16 through a connection hub or handle 22 that is connected in fluidcommunication with a sheath 38. The sheath 38 encloses radiating portion18 and feedline 20 to form a chamber 89 (FIG. 2) allowing one or morematerials such as, for example, fluid, gas, coolant, chemicals, saline,water, powdered solids, or any combination thereof, to circulate withinand/or occupy space within chamber 89. In some embodiments, connectionhub 22 may be coupled to a suitable supply pump (not shown) adapted tosupply fluid or coolant to chamber 89. In some embodiments, antennaassembly 12 may be embodied as, for example without limitation, aradiofrequency monopolar and/or bipolar electrode assembly, anultrasound transducer, laser fiber, a direct current (DC) heatingelement, or the like.

FIG. 2 illustrates a perspective view taken along line X-X of FIG. 1showing the radiating portion 18 of the antenna assembly 12 according toone embodiment of the present disclosure having a dipole antenna 40. Thedipole antenna 40 is coupled to the feedline 20 that electricallyconnects antenna assembly 12 to the generator 14. The dipole antenna 40includes a proximal portion 42 and a distal portion 44 interconnected ata feed point 46. The distal portion 44 and the proximal portion 42 maybe either balanced (e.g., of equal lengths) or unbalanced (e.g., ofunequal lengths). A dipole feed gap “G” is disposed between the proximaland distal portions 42 and 44 at the feed point 46. The gap “G” may befrom about 1 nun to about 3 mm. In one embodiment, the gap “G” maythereafter be filled with a dielectric material at the feed point 46.The dielectric material may be polytetrafluoroethylene (PTFE), such asTeflon® sold by DuPont of Willmington, Del. In another embodiment, thegap “G” may be coated with a dielectric seal coating.

With continued reference to FIG. 2, the antenna assembly 12 alsoincludes a choke 60 disposed around the feedline 20. The choke 60 may bea quarter-wavelength shorted choke that is shorted to the feedline 20 atthe proximal end (not illustrated) of the choke 60 by soldering or othersuitable methods.

Assembly 12 also includes a tip 48 having a tapered end 24 thatterminates, in one embodiment, at a pointed end 26 to allow forinsertion into tissue with minimal resistance at a distal end of theradiating portion 18. In those cases where the radiating portion 18 isinserted into a pre-existing opening, tip 48 may be rounded or flat. Thetip 48 may be formed from a variety of heat-resistant materials suitablefor penetrating tissue, such as metals (e.g., stainless steel) andvarious thermoplastic materials, such as poletherimide, and polyamidethermoplastic resins.

FIGS. 3A and 3B illustrate cross-sectional views of antenna assembly 12taken along line X-X of FIG. 1 according to various embodiment of thepresent disclosure. As shown by the illustrated embodiments, at least aportion of the feedline 20 and/or the radiating portion 18 may be formedfrom a semi-rigid and/or semi-flexible structure (e.g., coaxial cable)and includes an inner conductor 50 (e.g., wire) surrounded by an innerinsulator 52 with suitable dielectric properties. The inner insulator 52is, in turn, surrounded by an outer conductor 56 (e.g., cylindricalconducting sheath). The inner and outer conductors 50 and 56,respectively, may be constructed of copper, gold, stainless steel orother conductive metals with similar conductivity values. The metals maybe plated with other materials, e.g., other conductive materials, toimprove their properties, e.g., to improve conductivity or decreaseenergy loss, etc.

Since the radiating portion 18 and the feedline 20 are in direct contactwith materials such as fluid and/or solid, these components of theassembly 12 are sealed by a protective sleeve 63 (FIGS. 3A and 3B) toprevent any fluid seeping therein. This may be accomplished by applyingany type of melt-processible polymers using conventional injectionmolding and screw extrusion techniques. In one embodiment, a sleeve offluorinated ethylene propylene (FEP) shrink wrap may be applied to theentire assembly 12, namely the feedline 20 and the radiating portion 18.The protective sleeve 63 is then heated to seal the feedline 20 andradiating portion 18. The protective sleeve 63 prevents any materialfrom penetrating into the assembly 12.

Referring specifically now to FIG. 3A, one embodiment of the presentdisclosure is shown and includes separation members 91 a, 91 b disposedtransversely between protective sleeve 63 and an inner surface of sheath38 along at least a longitudinal portion of chamber 89 to sub-dividechamber 89 into semi-circular sub-chambers 89 a and 89 b. Sub-chambers89 a and 89 b are configured to retain first and second chemicals “A”and “B”, respectively, therein. Separation members 91 a, 91 b areconfigured to hold chemicals “A” and “B” within sub-chambers 89 a and 89b, respectively, in a seal-tight manner such that chemicals “A” and “B”are selectively prevented from contacting each other until needed tocontact each other.

In one embodiment, separation members 91 a, 91 b may be slidable ormovable, as discussed in further detail below with reference to FIG. 3C.In another embodiment, separation members 91 a, 91 b are formed of abreakable material, such as a breakable membrane, the structuralintegrity of which is compromised upon the application of a sufficientforce mechanically, electrically, or electro-mechanically thereto (e.g.,bending of semi-rigid feedline 20). In this scenario, once theseparation members 91 a, 91 b are broken or ruptured, contact betweenchemicals “A” and “B” is facilitated and, depending on the identity ofchemicals “A” and/or “B”, an endothermic or exothermic reaction ensuesto cool or heat the antenna assembly 12, respectively.

Chemical pairs used to generate an endothermic reaction through contact,reaction, dissolving, or mixture may include, without limitation, bariumhydroxide octahydrate crystals with dry ammonium chloride, ammoniumchloride with water, thionyl chloride (SOCl₂) with cobalt(II) sulfateheptahydrate, water with ammonium nitrate, water with potassiumchloride, and ethanoic acid with sodium carbonate. Chemical pairs usedto generate an exothermic reaction may include, without limitation,concentrated acid with water, water with anhydrous copper(II) sulfate,water with calcium chloride (CaCl₂), alkalis with acids, acids withbases, etc.

Referring specifically now to FIG. 3B, another embodiment of the presentdisclosure includes a concentric separation member 191 disposedlongitudinally through at least a portion of a cross-section of chamber89 to subdivide chamber 89 into longitudinal sub-chambers 189 a and 189b. Separation member 191 is substantially as described above withrespect to separation members 91 a, 91 b of FIG. 3A and will only bedescribed to the extent necessary to describe the differences betweenthe embodiments of FIGS. 3A and 3B. Similar to separation members 91 a,91 b described above with respect to FIG. 3A, sub-chambers 189 a and 189b are configured to hold chemicals “A” and “B” therein. Separationmember 191 may be slidable or movable, as discussed in further detailbelow with reference to FIG. 3C. In another embodiment, separationmember 191 is formed of a breakable material, such as a breakablemembrane, the structural integrity of which is compromised upon theapplication of a sufficient force mechanically, electrically, orelectro-mechanically thereto (e.g., bending of semi-rigid feedline 20).In this scenario, once separation member 191 is broken, contact betweenchemicals “A” and “B” is facilitated and, depending on the identity ofchemicals “A” and/or “B”, an endothermic or exothermic reaction ensuesto cool or heat the antenna assembly 12, respectively.

For purposes of simplifying the description of FIG. 3C to follow, FIG.3C will be described below with respect to the embodiment of FIG. 3B.However, the following description may also apply to the operation ofthe embodiment of FIG. 3A and, as such, any reference to separationmember 191 or sub-chambers 89 a and 89 b throughout the followingdescription may be substituted with reference to separation members 91a, 91 b and sub-chambers 89 a, 89 b, respectively.

Separation member 191 may, in certain embodiments, be configured to bemoved, actuated, slid, or the like, to permit or prevent communicationbetween sub-chambers 189 a and 189 b, respectively, such that contactbetween chemicals “A” and “B” is selectively facilitated or prevented.More specifically, separation member 191 includes a pair of interfacingsurfaces 95 a and 95 b that each include a plurality of apertures 93. Asillustrated by FIG. 3C, separation member 191 may be actuated such thatinterfacing surfaces 95 a and 95 b move relative to each other or,alternatively, such that one surface (e.g., 95 a) moves relative to astationary surface (e.g., 95 b). In either scenario, movement of surface95 a and/or surface 95 b operates to bring apertures 93 of both surfaces95 a, 95 b into and out of aligmnent with each other. That is, whenapertures 93 of surface 95 a are brought into substantial alignment withcorresponding apertures 93 of surface 95 b, sub-chambers 189 a and 189 bare in communication via apertures 93 such that contact betweenchemicals “A” and “B” is facilitated, Likewise, when apertures 93 ofsurface 95 a are brought out of substantial alignment with apertures 93of surface 95 b, communication between sub-chambers 189 a and 189 b isprevented.

Actuation of separation member 191 may be facilitated by an actuationmember (not shown) disposed on the exterior of the antenna assembly 12at a location suitable for operation by a user during an ablationprocedure (e,g., the connection hub 22). The actuation member, in thisscenario, is operably coupled to separation member 191 by any suitablenumber of configurations, components, mechanical connections, and/orcomponents (e.g., gears, links, springs, rods, etc.), and/orelectro-mechanical connections, configurations, and/or components suchthat separation member 191 may operate as intended. The actuation membermay be embodied as, for example without limitation, a button, slidebutton, knob, lever, or the like. For example, in the scenario whereinthe actuation member is a slide button, the slide button may beconfigured to slide longitudinally along the exterior of the antennaassembly 12 (e.g., along the connection hub 22) to actuate separationmembers 91 a, 91 b or separation member 191.

Referring to FIGS. 3A and 3B, the depiction of sub-chambers 89 a, 89 band 189 a, 189 b is illustrative only in that antenna assembly 12 mayinclude a plurality of sub-chambers, each of which is configured to holda chemical therein. In this scenario, an endothermic or exothermicreaction may be caused by the contact, mixture, dissolving, or reactionbetween three or more chemicals to thermally regulate the antennaassembly 12.

Referring now to FIG. 4, another embodiment of antenna assembly 12 isshown and includes a flexible sheath 291 disposed on at least a portionof the sheath 38 enclosing radiating portion 18 and feedline 20.Flexible sheath 291 includes an outer sub-chamber 295 a configured tohold chemical “A” and an inner sub-chamber 295 b configured to holdchemical “B”. Outer sub-chamber 295 a surrounds inner sub-chamber 295 band is separated therefrom at least partially by a breakable membrane293 (e.g., a shared surface between outer sub-chamber 295 a and innersub-chamber 295 b). Upon insertion of antenna assembly 12 into tissue“T”, as illustrated in FIG. 4, outer sub-chamber 295 a is configured toconform to the surface of antenna assembly 12 along a portion thereofinserted through tissue “T” and disposed within the insertion tract.Along the portion of antenna assembly 12 exterior to the tissue “T” oroutside the insertion tract, outer sub-chamber 295 a conforms to thesurface of tissue “T” (e.g., the patient's skin, a target organ, etc.).

In use, once antenna assembly 12 is inserted into tissue “T”, thestructural integrity of membrane 293 may be compromised to causecommunication between outer and inner sub-chambers 295 a and 295 b andfacilitate contact between chemicals “A” and “B”. As discussedhereinabove, contact between materials “A” and “B” causes an endothermicor exothermic reaction depending on the identity of materials “A” and/or“B”. In the scenario wherein an exothermic reaction results, forexample, the antenna assembly 12 may be heated sufficient to thermallymodify tissue in the insertion tract to stop bleeding upon removal ofantenna assembly 12 from tissue “T”. An exothermic reaction may also beused to simply heat the antenna assembly 12 if the antenna assembly 12becomes too cold. In the scenario wherein an endothermic reactionresults, for example, the antenna assembly 12 may be cooled sufficientto cool the insertion tract and stop bleeding upon removal of antennaassembly 12 from tissue “T”. An endothermic reaction may also be used tocool the surface of the tissue “T” facilitated by the conforming ofouter sub-chamber 295 a to the surface of the tissue “T” as describedhereinabove. An endothermic reaction may also be used to simply cool theantenna assembly 12 if the antenna assembly 12 becomes too hot.

The above-discussed system provides for the generation of endothermicand exothermic reactions within antenna assembly 12. The endothermicreaction removes the heat generated by the antenna assembly 12. Bykeeping the antenna assembly 12 and/or the ablation zone cooled, thereis significantly less sticking of tissue to the antenna assembly 12. Inaddition, the endothermic reaction acts as a buffer for the assembly 12and prevents near field dielectric properties of the assembly 12 fromchanging due to varying tissue dielectric properties. For example, asmicrowave energy is applied during ablation, desiccation of the tissuearound the radiating portion 18 results in a drop in tissue complexpermittivity by a considerable factor (e.g., about 10 times). Thedielectric constant (er′) drop increases the wavelength of microwaveenergy in the tissue, which affects the impedance of un-bufferedmicrowave antenna assemblies, thereby mismatching the antenna assembliesfrom the system impedance (e.g., impedance of the cable 16 and thegenerator 14). The increase in wavelength also results in a powerdissipation zone which is much longer in length along the assembly 12than in cross sectional diameter. The decrease in tissue conductivity(er″) also affects the real part of the impedance of the assembly 12.The fluid dielectric buffering according to the present disclosure alsomoderates the increase in wavelength of the delivered energy and drop inconductivity of the near field, thereby reducing the change in impedanceof the assembly 12, allowing for a more consistent antenna-to-systemimpedance match and spherical power dissipation zone despite tissuebehavior.

The described embodiments of the present disclosure are intended to beillustrative rather than restrictive, and are not intended to representevery embodiment of the present disclosure. Embodiments of the presentdisclosure may also be implemented in a microwave monopolar antenna orother suitable electrosurgical devices (monopolar or bipolar) and may beapplied with any suitable energy source (e.g., radiofrequency, directcurrent, microwave, laser, ultrasound, etc.) where, for example,reduction of heat and/or an increase in localized heating is desired.Various modifications and variations can be made without departing fromthe spirit or scope of the disclosure as set forth in the followingclaims both literally and in equivalents recognized in law.

What is claimed is:
 1. An energy-delivery assembly configured to deliverenergy from an energy source to tissue, the energy-delivery assemblycomprising: a radiating portion; a flexible sheath disposed over atleast a portion of the radiating portion, the flexible sheath definingan outer chamber and an inner chamber disposed within the outer chamber,wherein a distal end of the outer chamber extends past a distal end ofthe inner chamber; and a first composition disposed within the outerchamber and a second composition disposed within the inner chamber,wherein the outer chamber and the inner chamber are configured toselectively and fluidly communicate with each other to cause contactbetween the first composition and the second composition to cause one ofan endothermic reaction or an exothermic reaction.
 2. Theenergy-delivery assembly according to claim 1, wherein the outer chamberis separated from the inner chamber by a selectively rupturable membraneconfigured to break upon an application of at least one of a mechanical,electro-mechanical, or electrical force.
 3. The energy-delivery assemblyaccording to claim 1, further comprising a protective sleeve wrappedaround the radiating portion.
 4. The energy-delivery assembly accordingto claim 3, wherein the protective sleeve includes fluorinated ethylenepropylene shrink wrap.
 5. The energy-delivery assembly according toclaim 1, further comprising a coolant sheath enclosing the radiatingportion to define a space forming a coolant chamber.
 6. Theenergy-delivery assembly according to claim 5, further comprising athird composition disposed in the coolant chamber.
 7. Theenergy-delivery assembly according to claim 6, wherein the thirdcomposition is selected from the group consisting of a coolant, salineand water.
 8. The energy-delivery assembly according to claim 1, whereinthe first composition is selected from the group consisting of bariumhydroxide octahydrate, ammonium chloride, thionyl chloride, water andethanoic acid.
 9. The energy-delivery assembly according to claim 1,wherein the second composition is selected from the group consisting ofammonium chloride, water, cobalt sulfate heptahydrate, ammonium nitrate,potassium chloride, sodium carbonate, anhydrous copper sulfate, andcalcium chloride.
 10. The energy-delivery assembly according to claim 1,further comprising a feedline electrically coupled to the radiatingportion.
 11. An energy-delivery assembly configured to deliver energyfrom an energy source to tissue, the energy-delivery assemblycomprising: a radiating portion; an outer jacket enclosing the radiatingportion to define a coolant chamber; a flexible sheath disposed over atleast a portion of the outer jacket, the flexible sheath defining anouter chamber and an inner chamber disposed within the outer chamber,wherein a distal end of the outer chamber extends past a distal end ofthe inner chamber; and a first composition disposed within the outerchamber and a second composition disposed within the inner chamber,wherein the outer chamber and the inner chamber are configured toselectively and fluidly communicate with each other to cause contactbetween the first composition and the second composition to cause one ofan endothermic reaction or an exothermic reaction.
 12. Theenergy-delivery assembly according to claim 11, wherein the outerchamber is separated from the inner chamber by a selectively rupturablemembrane configured to rupture upon an application of at least one of amechanical, electro-mechanical, or electrical force.
 13. Theenergy-delivery assembly according to claim 11, further comprising aprotective sleeve wrapped around the radiating portion.
 14. Theenergy-delivery assembly according to claim 13, wherein the protectivesleeve includes fluorinated ethylene propylene shrink wrap.
 15. Theenergy-delivery assembly according to claim 11, wherein the firstcomposition is selected from the group consisting of barium hydroxideoctahydrate, ammonium chloride, thionyl chloride, water and ethanoicacid.
 16. The energy-delivery assembly according to claim 11, whereinthe second composition is selected from the group consisting of ammoniumchloride, water, cobalt sulfate heptahydrate, ammonium nitrate,potassium chloride, sodium carbonate, anhydrous copper sulfate, andcalcium chloride.
 17. The energy-delivery assembly according to claim11, further comprising a third composition disposed in the coolantchamber.
 18. The energy-delivery assembly according to claim 17, whereinthe third composition is selected from the group consisting of acoolant, saline, and water.
 19. The energy-delivery assembly accordingto claim 11, further comprising a feedline electrically coupled to theradiating portion.
 20. The energy-delivery assembly according to claim19, wherein the outer jacket encloses the feedline.